1. Field of the Invention
The present invention relates in general to a microwave oven and, more particularly, to an automatic thawing device of the microwave oven and a method for controlling the automatic thawing operation of the device.
2. Description of the Prior Art
A microwave oven is generally provided with an automatic thawing function for thawing of frozen food. The automatic thawing operation of the microwave oven is carried out by an automatic thawing device.
With reference to FIG. 1, there is shown in a block diagram a construction of a typical automatic thawing device of a microwave oven. The typical thawing device comprises a turntable 3 which is placed in a cooking chamber 1 of the microwave oven and rotates with frozen food 2 loaded thereon, thus to render the food 2 appropriately thawed. A weight sensor 4 is mounted under the turntable 3 and senses the weight of the food 2 loaded on the turntable 3. This weight sensor 4 is connected to a microprocessor 5 and outputs a food weight signal to this microprocessor 5. The microprocessor 5 calculates a thawing time, required to thaw the frozen food 2, by operation of the weight signal of the sensor 4 and outputs a thawing control signal for driving the microwave oven. This microprocessor 5 is connected to a time display 6 which displays the thawing time thereon in response to the thawing control signal of the microprocessor 5. An output drive unit 7 is connected to the microprocessor 5 and outputs a drive signal in response to the thawing control signal of the microprocessor 5, thus to drive a magnetron 8 of the oven. This magnetron 8 generates an electromagnetic wave of high frequency or a microwave for the thawing time calculated by the microprocessor 5.
In FIG. 1, the reference numeral 9 denotes an exhaust port for exhausting vapor or gas generated from the food 2 in the cooking chamber 1 to the outside of the oven.
FIG. 2 is a flowchart of a method for control of the thawing operation of the above thawing device.
When the frozen food 2 is loaded on the turntable 3 in the cooking chamber 1 in order to be automatically thawed, the weight sensor 4 under the turntable 3 senses weight of the food 2. Upon sensing the food weight, the sensor 4 outputs the food weight signal to the microprocessor 5 where the weight signal is operated in order to calculate the thawing time required in thaw of the frozen food 2.
The microprocessor 5 in turn outputs the thawing control signal to both the time display 6 and the output drive unit 7. Upon reception of the thawing control signal, the time display 6 displays the thawing time thereon while the drive unit 7 outputs a signal for driving the magnetron 8. Accordingly, the magnetron 8 is oscillated and generates the electromagnetic wave of high frequency for the thawing time calculated by the microprocessor 5, thus to thaw the frozen food 2 in the rotating turntable 3. If briefly described, the typical thawing device calculates the thawing time in accordance with weight of frozen food and generates the electromagnetic wave of high frequency for the calculated thawing time, thus to thaw the frozen food.
The method for control of the frozen food thawing operation of the typical thawing device will be described in detail with reference to the flowchart of FIG. 2.
First, it is checked whether an automatic thawing key of a control panel was pushed in order to select an automatic thawing function. When the automatic thawing key has not been pushed, another function of the microwave oven is carried out. However, when the automatic thawing key was pushed, it is checked whether a food weight signal of the weight sensor 4 has been inputted. When the weight signal has been inputted, the weight signal is operated in order to calculate the thawing time for the frozen food 2. Here, the thawing time T.sub.R results from addition of 1 to a result of multiply of the food weight W to 0.6, that is, the thawing time T.sub.R is represented by the following equation. EQU T.sub.R (min.)=(W.times.0.6)+1.
When the thawing time is calculated by the above operation of the food weight signal, it is checked whether a door of the microwave oven has been closed. When the door has been closed, a relay (not shown) is turned on in order to start the desired thawing operation by oscillating the magnetron 8 for the thawing time. However, when the door is not closed, a continued function is carried out.
As described above, the typical automatic thawing device senses weight of frozen food and calculates an appropriate thawing time by operation of food weight signal using a preset experimental data. This typical automatic thawing device and the control method thereof is disclosed in, for example, Korean Patent Laid-open Publication No. 92-1987 and Korean U. M. Publication No. 89-6080.
However, the above thawing device and its control method have a problem that the weight sensor should be provided in the device for sensing the food weight in the thawing operation, thus to increase cost due to its expense and to cause fraction defective due to its structural complexity. The mounting of the weight sensor under the turntable is also attended with a complex mounting structure, thus to deteriorate reliability of the microwave oven.
Since the typical automatic thawing device and its control method carry out the thawing operation only in accordance with sensed weight of the frozen food regardless of kind and frozen level of the food to be thawed, the frozen food may be slightly cooked or deficiently thawed. Furthermore, when the frozen food with a dish is unconsciously loaded on the turntable, the device carries out the thawing operation for an excessive time calculated on the basis of the total weight of both the food and the dish, thus to slightly cook the food and to deteriorate the reliability of the microwave oven.